Generally, acrylate-styrene-acrylonitrile based graft copolymers (hereinafter referred to as acrylate-styrene-acrylonitrile polymers) as impact modifiers for thermoplastic resins are made of multilayered copolymer graft particles, namely, in a core-shell structure. In order to enhance impact strength, acrylic rubber is mainly used as the core, and, in order to enhance colorability and dispersibility for a matrix resin, styrene-acrylonitrile based copolymers including a styrene monomer and acrylonitrile monomer (hereinafter referred to as SAN), etc. may be used as the shell.
Research to enhance impact characteristics through increase of soft rubber core parts and decrease of hard shell parts of acrylic impact modifiers having a core-shell structure is underway. However, when hard shells are decreased, latex stability and coagulation characteristics are deteriorated, and processing characteristics, etc. are affected. Therefore, technology for satisfactorily enveloping a soft rubber core with a small amount of a hard shell part is an important factor to enhance impact resistance, coagulation characteristics, processability, etc.
Accordingly, a variety of research regarding methods of satisfactorily enveloping a core with a shell or methods to enhance coagulation characteristics is underway. For example, in order to satisfactorily graft a shell onto a core, a compound having two double bonds or more that have different monomer reactivity was used as a grafting agent. However, when the grafting agent is used in a large amount, it functions like a cross-linking agent, and thus, impact strength may be decreased.
In addition, graft polymerization is performed on a core surface. Accordingly, when the grafting agent remains within the core, the total of the grafting agent might not participate in grafting reaction. Double bonds having low reactivity of the grafting agent remaining in the core may cause undesired side reaction, thereby leading to property deterioration (by causing defects/dents).
Recently, in order to prevent distortion and breakage of a rubber by hardening a rubber core in a multilayered copolymer graft particle, a hard seed was introduced.
Meanwhile, research into methods of satisfactorily enveloping a seed with a core or methods of enhancing coagulation characteristics is underway. For example, such that a core is satisfactorily grafted onto a seed, a compound having two double bonds or more that have different monomer reactivity was used as a grafting agent. However, when the grafting agent is used in a large amount, it functions like a cross-linking agent, and thus, impact strength may be decreased.
In addition, when the grafting agent remains within the seed, the total of grafting agent might not participate in grafting reaction, and double bonds having low reactivity with the grafting agent that remains within the seed cause undesired side reaction, thereby leading to property deterioration (by causing defects/dents).
Recently, emotional levels for quality of consumers are increasing, and thus, demand for resins that are not aged during much longer time is increasing. In particular, compositions having enhanced weather resistance are required in exterior materials and roofs of structures, computer housings, keyboards, electric devices, vehicle components, etc.
However, weather resistance is enhanced due to addition of additives, increase of the amount thereof and modification of combinations thereof, which is a major factor of production cost increase. In addition, when additives, etc. are jetted to gas during a process such as extrusion/injection, impurities, etc. may be observed on a surface of a molded product, and thus, commercial value of a molded product may be deteriorated.
In addition, an activating solution is used to initiate redox during polymerization, but functions as an impurity after processing, thereby deteriorating weather resistance.
Accordingly, research into technology to overcome the advantages described above is required.